1. Field of the Invention
The present invention relates to a driving apparatus and a driving method for an electron emission display. More particularly, the present invention relates to a driving apparatus and a driving method for an electron emission display in which a pulse width frequency of an output signal is switched fewer times, reducing total power consumption.
2. Discussion of Related Art
In a general flat panel display (FPD), a container is formed by sealing two substrates with a lateral wall therebetween and appropriate materials are arranged within the container to realize display of a desired image. The demand for FPDs has been increasing. Accordingly, various FPDs, e.g., a liquid crystal display (LCD), a plasma display panel (PDP), an electron emission display, etc., have been developed and employed.
The electron emission display uses an electron beam to make a fluorescent material emit light, similar to the operation of a cathode ray tube (CRT). The electron emission display has the good qualities of both the CRT and the FPD, while consuming less power and displaying an image without distortion. Further, the electron emission display is anticipated as a next generation display because it fulfills numerous requirements, e.g., fast response time, high brightness, fine pitch, thinness, etc.
In general, an electron emission device uses a hot cathode or a cold cathode as an electron source. Cold cathode devices include a field emitter array (FEA) type, a surface conduction emitter (SCE) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, a ballistic electron surface emitting (BSE) type, etc.
The electron emission display typically has a triode structure of a cathode electrode, an anode electrode and a gate electrode. In more detail, the cathode electrode, generally used as a scan electrode, is formed on a substrate. An insulating layer formed with a hole and the gate electrode, generally used as a data electrode, are sequentially formed on the cathode electrode. Then, an emitter is formed as the electron source within the hole and in contact with the cathode electrode.
In the electron emission display with this configuration, the emitter emits electrons by focusing a high electric field thereon, which can be explained by the quantum tunneling effect. The electrons emitted from the emitter are accelerated by a voltage applied between the cathode electrode and the anode electrode, and collide with red, green and blue (RGB) fluorescent materials provided on the anode electrode, so that the fluorescent materials emit light, thereby displaying a predetermined image.
The brightness of an image displayed as the emitted electrons collide with the fluorescent materials is varied according to values of an input digital video signal. In more detail, the digital video signal has a value of 8 bits corresponding to each of red (R), green (G) and blue (B) data. That is, the digital video signal has a value ranging from 0 (00000000(2)) to 255 (11111111(2)). Thus, 256 gray levels can be represented depending on 256 values of the digital video signal and the brightness is represented by an associated digital value.
In general, a pulse width modulation (PWM) method or a pulse amplitude modulation (PAM) method is used to control the brightness represented by the values of the digital video signal.
The PWM method modulates the pulse width of a driving waveform applied to the data electrode in accordance with the digital video signals input from a data electrode driver. When the digital video signal having a value of 255 is input within the allowable maximum on-time, the pulse width is maximized, thereby maximizing the brightness. When the digital video signal has a value of 127, the pulse width is reduced to half of the maximum pulse width, thereby controlling the brightness correspondingly.
The PAM method keeps the pulse width constant regardless of the input digital video signal, and modulates the pulse voltage level, i.e., the pulse amplitude of the driving waveform applied to the data electrode in accordance with the input digital video signal, thereby controlling the brightness.
FIG. 1 illustrates waveforms of input/output signals when a polarity control signal has a high level in a conventional electron emission display. As shown therein, input/output signals of the column driver include a horizontal synchronous signal Hsync, a polarity control signal Pol having a high level, a video data input signal Input Data, which is input to a data driver, and a video data output signal Driver Output, which is output from the data driver.
The video data input signal is input in accordance with the horizontal synchronous signal as a periodic signal for a data line. Here, the video data input signal is converted to have a corresponding pulse width by a PWM method.
For example, when video data input signals having values of “128”, “64”, “200” and “100” are input in sequence, the video data input signals of 8 bits are converted to respective corresponding pulse widths of “Ta”, “Tb”, “Tc” and “Td”. Here, the pulse widths of “Ta”, “Tb”, “Tc” and “Td” correspond to brightness levels, respectively. In this example, “Ta”=“2 Tb”, and “Tc”=“2 Td”.
Further, the polarity control signal is used for controlling the polarity of the video data output signal output from the data driver. For example, when the polarity control signal has a high level and a signal output from the data driver has a low level, the video data output signal has a high level.
FIG. 2 illustrates waveforms of input/output signals when the polarity control signal has a low level in the conventional electron emission display. As shown therein, input/output signals of the column driver include a horizontal synchronous signal Hsync, a polarity control signal Pol having a low level, a video data input signal Input Data, which is input to a data driver, and a video data output signal Driver Output, which is output from the data driver.
The video data input signal is input in accordance with the horizontal synchronous signal as the periodic signal for the data line. Here, the video data input signal is converted to have a corresponding pulse width by a PWM method.
For example, when video data input signals having values of “128”, “64”, “200” and “100” are input in sequence, the video data input signals of 8 bits are converted to have pulse widths of “Ta”, “Tb”, “Tc” and “Td” corresponding to the values of “128”, “64”, “200” and “100”. Here, the pulse widths of “Ta”, “Tb”, “Tc” and “Td” correspond to brightness levels, respectively. In this example, “Ta”=“2 Tb”, and “Tc”=“2 Td”.
Further, the polarity control signal is used for controlling the polarity of the video data output signal output from the data driver. For example, when the polarity control signal has a low level and a signal output from the data driver has a high level, the video data output signal has a low level.
When the video data output signal has the pulse widths of “Ta”, “Tb”, “Tc” and “Td”, a switching frequency is determined in accordance with the resolution of the video data output signal. That is, the switching frequency becomes higher as the resolution increases, thereby increasing power consumption.
In more detail, in the driving apparatus for the electron emission display having a matrix structure, a video signal applied to a column line is converted to have a pulse width corresponding to a predetermined voltage level and the polarity is switched in proportion to a horizontal resolution. Thus, the number of polarity switches of the video signal corresponds to the horizontal resolution.
Here, the power consumption in a column electrode of the electron emission display can be calculated by the following equation.P=c×ΔV2×f Where, P is power consumption in the column electrode, c is a line capacitance of a display panel, V is a voltage variation of the video signal, and f is a switching frequency.
Thus, the conventional driving method for the electron emission display consumes more power as the resolution increases, i.e., in proportion to the number of times the pulse width is switched.